Field of the Invention
The present invention is broadly concerned with temperature sensors and temperature measurement systems permitting wireless temperature measurement of various objects during heating or cooling thereof. More particularly, the invention is concerned with such sensor and systems, and especially those designed for heating of food servingware, such as food plate domes. The sensors include a transponder and a proximal parasitic antenna, the latter having a temperature-sensitive transducer operable to change the impedance value of the parasitic antenna when the object being temperature-sensed reaches a predetermined temperature for transducer operation.
Description of the Prior Art
Remote, wireless temperature measurement systems employing identification technologies exist in the prior art, see U.S. Pat. No. 6,320,169, which is incorporated by reference herein in its entirety. The '169 patent describes Radio Frequency identification (RFID) labels or tags physically connected to one or more thermal switches, where the thermal switch(es) are in contact with an object whose temperature is to be remotely measured. Interrogating electromagnetic signals are generated, which are received by the RFID tag, which in turn generates reply signals. However, when the object temperature reaches or exceeds a pre-set temperature, the thermal switch(es) disconnect the RFID antenna so that no reply signals are generated. This is interpreted by the system as a condition where the object has reached or exceeded the pre-set temperature.
There are several disadvantages with the tag/switch combination and associated measurement system of the '169 patent. First, the tag/switch combination is difficult to incorporate within an object whose temperature is to be measured. The physical connection between the tags and switches is inherently delicate, making use of fine connection wires and connectors soldered or affixed to the tag. As such, it is very difficult to injection mold such a tag/switch combination within an object. Second, if the connection between the switch and tag is short in length so as to facilitate manufacturing, the tag may be too close to the object to be measured to allow for good communication with the tag, owing to antenna de-tuning by the object, especially if the object is made from an electrically conducting material. Conversely, if the connections are lengthened so as to enhance communications by eliminating any adverse effects from the object, the difficulty of incorporation into the object increases. Third, the fact that the tag is connected to the switch means that thermal energy from the object in contact with the switch will conduct or radiate to the tag, either through the connecting leads or simply by conduction through adjacent matter. Thus, should the tag/switch combination be used to measure high object temperatures, the integrated circuitry of the tag may be destroyed or tag communication may be disrupted.
Therefore, it would be a decided advantage to provide a remote temperature measurement system whose label or tag can be thermally insulated from the object whose temperature is to be measured. In such a case, object temperatures can be measured which well exceed the label's rated operating temperature. Moreover, labels or tags having integrated circuits and extensive memory storage can be employed, allowing storage and update of digital information on the associated labels or tags. This storage and updating of digital information at high operating temperatures allows additional features beyond simple temperature measurement, such as storage of heating instructions, point-of-sale information, and more.
It would also be advantageous to provide remote temperature measurement systems having labels or tags physically separate from any required temperature sensor or thermal switch, thereby eliminating the delicate tag/switch connections of the prior art. Separate labels or tags could be easily incorporated into an object so that the electromagnetic coupling between the labels or tags and an interrogator (e.g., an RFID reader) is not compromised by the adjacent object material.
U.S. Pat. No. 6,172,608, incorporated by reference herein in its entirety, discloses an enhanced range transponder system including a transponder label electromagnetically coupled to a parasitic antenna, the latter being simultaneously electromagnetically coupled to the interrogator. However, the transponder system of the '608 patent is not designed to measure object temperatures, either at single or multiple temperature measurement locations on an object.